Pneumatic tube carrier systems are a well-known means for the automated transport of materials between, for example, an origination location to any one of a plurality of destination locations. A typical system includes a number of pneumatic tubes interconnected in a network to transport carriers between a number of user stations. Various blowers and transfer units provide the force and path control means, respectively, for moving the carriers through and from tube-to-tube within the system. One type of transfer unit allows pneumatic carries to be moved from a first pneumatic tube to a second pneumatic tube in order to route the pneumatic carrier between locations, or stations, in the network.
The pneumatic tubes that connect the various locations may be arranged in any manner that allows the carriers to be transferred between various stations. Generally, an individual station is interconnected to the network by a single pneumatic tube. In this arrangement, such a single pneumatic tube is utilized to carry carriers to and from the station. Other portions of the network are often interconnected with dedicated pneumatic tubes. That is, two locations within the system may be interconnected by two dedicated pneumatic tubes where a first tube carries outgoing pneumatic carriers and a second tube (e.g., a parallel tube) carries incoming pneumatic carriers.
As will be appreciated, locations having a single pneumatic tube connection can only carry a pneumatic carrier in a single direction at a time. To avoid gridlock in the system, it is desirable to remove carrier from such single tube connections as soon as possible. For instance, when delivering a carrier to a station via a single tube connection, the station may be designed such that the carrier is removed from the tube immediately upon arrival (e.g., the carrier falls into a receiving bin). The tube may thus be cleared for additional transactions. However, a more difficult situation arises when a carrier is being sent from a single tube location. Depending upon network traffic, a route to an intended destination may not be immediately available. Further, if the carrier remains in a single tube awaiting launch, the carrier may interfere with incoming traffic.
Accordingly, it may be desirable to send an outgoing carrier to a location within the network where the carrier may be temporarily stored until the carrier can be processed and sent to its intended destination. However, stopping a carrier at such a location within a pneumatic network can lead to various complications. One particular complication is that the carrier, once stopped, may become stuck within a pneumatic tube within the network and thereby require manual removal. That is, it may be difficult to reinitiate movement of a stationary carrier within a pneumatic tube. Previous systems have attempted to utilize a conveyor belt system to reinitiate movement of stationary carriers. However, such systems have proved mechanically difficult to manufacture, pneumatically seal and maintain. Further, due to the constraints of operating a conveyor belt within a pneumatic tube, the contact area between such a conveyor belt and a pneumatic carrier is generally small and may fail to provide enough force to initiate movement of a stationary carrier thereby requiring manual intervention. In this regard, failure to reinitiate movement of a stationary carrier may require that a portion of the network or the entire network to be shut down for maintenance.